FAA Commercial Pilot Airplane (CAX)Aerodynamics and PerformanceHard
An airplane's engine fails while the pilot is circling to reach a nearby airport rather than gliding in a straight line. The pilot wants to remain airborne as long as possible rather than cover maximum distance. Which airspeed should the pilot fly?
- AMinimum sink speed, which is slower than best glide speed
- BNever-exceed speed (Vne)
- CManeuvering speed (Va)
- DBest glide speed (L/D max)
Show answer & explanationAnswer & explanation
Correct answer: A. Minimum sink speed, which is slower than best glide speed
Best glide speed (L/D max) maximizes glide distance, but minimum sink speed—slightly slower than best glide—minimizes the rate of descent, maximizing time aloft at the cost of some glide distance. Since the pilot's goal is maximum endurance while circling, minimum sink speed is correct.
Why the other options are wrong
- B. Vne is a structural limit unrelated to glide performance goals.
- C. Va relates to structural protection, not glide performance.
- D. Best glide speed maximizes distance, not time aloft.
Minimum Sink Speed vs Best Glide Speed
Minimum sink speed minimizes descent rate for maximum time aloft, while best glide speed (L/D max) maximizes glide distance; minimum sink speed is slower than best glide speed.
- Best glide speed = L/D max, maximizes distance covered.
- Minimum sink speed is slower, maximizes time aloft (endurance).
- Choose minimum sink when time, not distance, is the priority (e.g., circling to lose altitude near a field).
Memory trick: Slow for time, L/D max for distance.